Method for fabricating a choke with adjustable air gap and choke produced thereby

ABSTRACT

A method for fabricating a choke wherein the air gap provided with an insert can be adjusted by core portions displaceable relative to one another. The relatively displaceable core portions are clamped between a floor with upstanding side edges and a resilient hood having sidewalls, the hood being displaceable towards the floor. After adjusting the desired air gap the sidewalls of the hood are fastened as by welding with the side edges of the floor, so that the air gap insert is continuously maintained under a constant stress or load.

United States Patent [1 1 Meili [11] 3,889,360 1 June 17, 1975 METHOD FOR FABRICATING A CHOKE WITH ADJUSTABLE AIR GAP AND CHOKE PRODUCED THEREBY [75] Inventor: Ernst Meili, Uster, Switzerland [73] Assignee: F. Knobel Elektro-Apparatebau AG,

Ennenda, Switzerland [22] Filed: June 8, 1973 [21] Appl. N0.: 368,123

[30] Foreign Application Priority Data June 9, 1972 Switzerland 8668/72 Jan. 18, 1973 Switzerland 698/73 [52] US. Cl. 29/593; 336/134; 324/59 [51] Int. Cl. G011 27/16 [58] Field of Search 29/592, 593, 203 R, 203 D; 336/134, 178; 324/59; 73/1 B [56] References Cited UNITED STATES PATENTS 2,064,772 12/1936 Vogt 336/134 2,674,721 4/1954 Jackson et al. 336/134 2,835,876 5/1958 Hammond 336/134 3,267,400 8/1966 Craige 336/134 3,619,434 11/1971 Blastic et al. 29/593 3,622,928 11/1971 Lee 336/134 FOREIGN PATENTS OR APPLICATIONS 717,342 1/1942 Germany 336/178 421,353 12/1934 United Kingdom 336/134 Primary ExarninerC. W. Lanham Assistant ExaminerDan C. Crane Attorney, Agent, or Firm-Waters, Schwartz & Nissen [5 7] ABSTRACT A method for fabricating a choke wherein the air gap provided with an insert can be adjusted by core portions displaceable relative to one another. The relatively displaceable core portions are clamped between a floor with upstanding side edges and a resilient hood having sidewalls, the hood being displaceable towards the floor. After adjusting the desired air gap the sidewalls of the hood are fastened as by welding with the side edges of the floor, so that the air gap insert is continuously maintained under a constant stress or load.

6 Claims, 6 Drawing Figures PATENTEDJUH 17 I975 SHEET 1 3,889,360

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PATENTEDJUN 1 1 m5 3 a as .36 0 SHEET 2 Fig. 6

1 METHOD FOR FABRICATING A CHOKE WITH ADJUSTABLE AIR GAP AND CHOKE PRODUCED THEREBY BACKGROUND OF THE INVENTION The present invention relates to a new and improved method of fabricating a choke in which the air gap provided with an insert is adjustable by core portions which are displaceable with respect to one another.

With such chokes the air gap insert consisting of nonmagnetic material is squeezed together to the desired thickness during the tuning operation and thus forms a fixed support for the air gap. This support is only effective when the insert is continuously maintained under pressure, wherefore the choke must be provided with a resilient element which, following tuning, maintains the insert under pressure. To achieve rational fabrication of the choke it is furthermore necessary that the air gap can be adjusted within wide limits without changing magnetic parts, housing parts, and the like.

There is already known to the art a method for the fabrication of such type choke in which a resilient hood member is flanged with a floor or bottom portion. However, the flanging operation does not permit any accommodation to different sizes of the air gap. It has the drawback that it is not capable of compensating mass produced tolerances of the hood and floor, so that the resilient action of the hood becomes questionable and the adjusted choke can change. Hence, maintaining a prescribed impedance value within a narrow tolerance is not possible.

According to another prior art technique for the fabrication of a choke a resilient floor portion is engaged with a magnetic core. Since in this case, however, the floor portion only possesses an extremely small spring deflection or displacement path the air gap cannot be varied or adjusted within wide limits. For each desired air gap thickness there is thus required a change of the floor.

SUMMARY OF THE INVENTION I Hence, it is a primary object of the present invention to provide an improved method of fabricating a choke with an adjustable air gap which is not associated with the aforementioned drawbacks and limitations of the prior art proposals.

Another object of the present invention relates to chokes fabricated in accordance with the method aspects of this invention.

Now in order to overcome the aforementioned drawbacks the method of this development for the fabrication of a choke of the previously mentioned type is manifested by the features that the core portions which are displaceable relative to one another are clamped between a floor having upstanding side edges and a resilient hood which is displaceable towards the floor and which hood has side walls. following adjustment of the desired air gap the sidewalls of the hood are welded with the side edges of the floor, so that the air gap insert is continuously maintained under a constant stress or load.

Advantageously, the upper wall of the hood which ascends to both sides from its central region, during clamping together of the hood and floor, is pressed flat in order to exert a predetermined pressure upon the air gap insert.

Previously when. fabricating the choke according to the method of the invention the adjustment of the air longer is increased after reaching the desired impedgap insert round copper wires, then the undesired afterflow or post-flow of the material amounts to approximately 5 to 10% of the strived for impedance. The postflow of material is also dependent upon the thickness of the squeezed or clamped insert, so that during pronounced squeezing this post-flow effect is correspondingly greater. In any case there arises an impedance error which is in the order of several percent, for instance about 57? in a stray field, a value impermissibly high for precision chokes.

The problem of the flow of the air gap material can be overcome if the air gap insert is subjected to a vibrational force or impacts for such length of time until the desired impedance value has been attained. However, the technique employing impacts is not practical since it is much too slow. The use of a vibrating force does indeed allow for very rapid tuning, however it is practically impossible to suddenly interrupt the tuning operation when the desired impedance value has been reached, so that here also there remains a certain disturbing residual error.

These imperfections should be overcome by the method of this development in that the choke after setting or adjustment of the air gap and welding of the side walls of the hood with the side edges of the floor is inserted into a tuning device in which a roller acts with adjustable pressure upon the choke and the roller or the choke are displaced in the lengthwise direction of the choke, so that the insert is continuously squeezed or compressed due to the rolling motion of the roller upon the choke. The pressure on the roller of an impedance measuring device connected with the choke is controlled such that upon reaching the reference or rated value, the pressure acting upon the roller is diminished and there is obtained an exact fine tuning of the choke. Squeezing or compression of the air gap insert therefore in this case does not occur through simultaneous compression or impacting along the entire length of the choke, rather by a rolling action undertaken by a roller so that the pressure, by means of which the wire is squeezed or compressed together, progresses along the wire and upon cessation of the pressure there is attained an exact fine tuning with an impedance error of less than 1%.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood and objects other than those set forth above, will become apparent ,.-when consideration is given to the following detailed v description thereof. Such description makes reference to the annexed drawings wherein:

FIG. 1 is a longitudinal sectional view ofa choke fab- I used in the fabrication of the choke prior to assembly of the choke;

FIG. 4 is a perspective view of a choke produced according to the method aspects of the invention;

FIG. Sis a cross-sectional view of the choke depicted -in FIG. 4 together with a roller acting upon the choke for fine tuning; and

FIG. 6 illustrates details of a tuning device for the choke for carrying out certain aspects of the method of this invention. I

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawings, the exemplary embodiment of choke depicted in FIGS. 1 and 2 will be recognized to comprise three core portions or components 1, 2 and 3 and a coil 4. The core portion 3 is displaceable relative to the core portions 1 and 2 in order to be able to adjust the air gap 5 located therebetween. In the air gap 5 there is located an insert which here is shown to consist of two lacquer coated copper wires 6, which for the'purpose of facilitating assembly, are fixed upon an adhesive foil 7. The core portions 1, 2 and 3 are clamped between a floor or bottom 8 having upstanding side edges 9 and a hood 10 with side walls 11.

As bestseen by referring to FIG. 3 the upper wall of the hood 10, prior'to assembly of the choke, ascends or slopes upwardly to both sides from the center of such hood. During clampingtogether of the hood 10 and the floor 8 this upper wall of the hood is pressed flat, and due to the resilient action'of the hood a certain pressure is exerted upon theair gap insert, that is the copper wires 6, so that a desired air gap and therefore a desired impedance of the choke can be adjusted. After this adjustment the side walls of the hood are fastened as by'welding with the side edges of the floor, to which end there is preferably employed a projection or bulge weld. As a result the air gap insert is continuously maintained under constant load or stress. As tests have shown even if the choke after the tuning operation is impregnated in vacuum the-impedance due to the impregnation only increases by about 3 0/00.

Now in order to be'able to carry out fine tuning of such type choke as depicted in FIGS. 4 and 5 such is inserted into the tuning device or equipment depicted in FIG. 6. The choke is mounted upon a carriage 12 which is lengthwise displaceable along a support 13. Operatively connected with the carriage 12 is a piston rod 14, the piston 15 of which is displaceable within a cylinder 16. Conduits or lines 17 and 18 are operatively connected with the cylinder 16. A roller or roll 19 acting upon the hood 10 of the choke is mounted by means of a shaft 20 at one arm of the angle lever 21. This angle lever 21 is rotatably mounted about a pivot pin 22 at a bracket 23 of a column 24. A piston rod 26 engages through the agency of a pin at the end of the other arm of the angle lever 21. The piston 27 of the piston rod 26 travels in a cylinder 28 at which there is also connected two conduits or lines 29 and 30. The

tuning device is additionally equipped with a contact mechanism 31 at which there are automatically connected the contact tabs or plugs 32 of the choke coil 4 upon insertion of the choke. Conductors 33 lead from I the contact mechanism 31 to any suitable and therefore merely schematically illustrated impedance measuring instrument or device 50, by means of which there can be controlled the infeed of compressed air or oil or some other suitable pressurized medium to the cylinder 28.

With the foregoing in mind there will now be considered the operation of the previously described tuning device which is as follows:

After insertion of a choke into the equipment, compressed air or oil is admitted via the conduit or line into the cylinder 28. Consequently, a pressure is exerted upon the roller 19 due to the action of the piston 27 via the angle lever 21 and this pressure acts upon the lengthwise extending groove of the hoodul 0. This pressure is transmitted via the sheet metal lamellaeof the core portion 3 to the copper wires 6 located at the air gap 5, so that the wires 6 are squeezed or compressed. At the same time and owing to the introduction of compressed air or oil through the conduit or line 17 into the cylinder 16 the piston 15 is displaced in the direction of the arrow and the choke is drawn through or displaced beneath the roller or roll 19, wherein the length of the path through which the choke moves corresponds to the length of a squeezed together wire section. Due to the continuous squeezing of the copper wires 6 the size of the air gap 5 and therefore the impedance of the coil 4 is continuously changed. If the impedance of the choke has'attai ned a predetermined value then due to the action of the impedance measuring device 50 the pneumatic or hydraulic piston 26 is reversed, so that the roller 19 is raised from the choke and the impedance is no longer altered.

The pressure exerted'upon the roller 19 is advantageously adjusted such that almost the entire length of the wires 6 must'be rolled in order to attain the desired impedance value.'This is undertaken'foi' two reasons: one is to ensure that the thickness of theair gap -.over the entire length of each wire is as constantin size as possibleQin order that the induction in the air gap and in the iron core is asuniform as possible. The other reason concerns the tuning accuracy. Upon reaching. the desired impedance-the lengthwise movement of the choke cannot be suddenly stopped and the pressure exerted upon the roller is also not suddenly reduced to null. Due to the thus realized stopping path and the post-flow of the wire material during constant pressure there occurs a compensation error. This compensation error becomes percentually negligible with a long roller path. L v

The pressure exerted upon the roller 19 also can be chosen to be so small that a second throughpass of the choke beneath the roll or roller for obtaining the desired impedance value is necessary, whereby'the direction of movement of the piston 15 and the choke, after the first pass, automatically is reversed and the exerted pressure is advantageously increased. AS a result the tuning error can be further reduced. In principle more than two passes are possible, but in actual practice one is generally satisfied with two passes since otherwise the tuning time becomes 'much too long for rational fabrication purposes. Therefore those chokes are rejected which anyway cannot be tuned during a second pass."As experience has shown such chokes are anyway associated with a manufacturing defect. According to a practical application of the method with the described tuning device there could be obtained cycle times of about 3 seconds.

Since with the method of the invention, owing to the rolling operation undertaken by a roller, there is only necessary a relatively small force in order to attain the specific pressure required for the desired squeezing or compression of the wires, there is realized the advantage that the tuning device is of relatively small constructional size and can be easily incorporated into the manufacturing assembly line.

After the aforedescribed fine tuning of the choke such is also advantageously impregnated with a synthetic resin as is known in the art.

Instead of, as with the described embodiment, drawing the choke in the lengthwise direction beneath the roller it would also be possible to displaceably arrange the roller with its support mechanism, so that it can be moved in the lengthwise direction of the choke over the choke and thus rolls upon the choke,

While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope of the following claims.

What is claimed is:

1. A method for fabricating a ballast wherein the air gap provided with an insert can be adjusted by core portions displaceable with respect to one another, the improvement comprising the steps of: clamping the relatively displaceable core portions between a floor provided with upstanding side edges and a resilient hood having side walls and which hood can be displaceable in the direction of such floor, adjusting a desired air gap, fastening the side walls of the hood with the side edges of the floor, so that the air gap insert is continuously maintained under a substantially constant stress, the fastening step including welding the side walls of the hood with the side edges of the floor, inserting the ballast into a tuning device after adjustment of the air gap and welding of the side walls of the hood with the side edges of the floor, applying a roller of the tuning device so as to act upon the ballast with adjustable pressure, effecting relative displacement between the roller and the ballast in the lengthwise direction of the ballast, to thereby continuously squeeze together the insert by the rolling motion of the roller at the ballast, and controlling the pressure at the roller by an impedance measuring device connected with the ballast such that upon attaining a rated impedance the pressure acting at the roller is diminished and thereby obtaining an exact fine tuning of the ballast.

2. The method as defined in claim 1, including the step of applying the contact pressure of the roller by a pressurized fluid medium operated piston.

3. The method as defined in claim 1, including the step of applying the contact pressure of the roller by a lever arrangement.

4. The method as defined in claim 1, further including the step of raising the roller away from the ballast upon attaining the rated impedance of the ballast.

5. The method as defined in claim .1, including the step of displacing the ballast in lengthwise direction beneath the roller.

6. The method as defined in claim 5, including the step of employing pressurized fluid operated piston means for displacing the ballast. 

1. A method for fabricating a ballast wherein the air gap provided with an insert can be adjusted by core portions displaceable with respect to one another, the improvement comprising the steps of: clamping the relatively displaceable core portions between a floor provided with upstanding side edges and a resilient hood having side walls and which hood can be displaceable in the direction of such floor, adjusting a desired air gap, fastening the side walls of the hood with the side edges of the floor, so that the air gap insert is continuously maintained under a substantially constant stress, the fastening step including welding the side walls of the hood with the side edges of the floor, inserting the ballast into a tuning device after adjustment of the air gap and welding of the side walls of the hood with the side edges of the floor, applying a roller of the tuning device so as to act upon the ballast with adjustable pressure, effecting relative displacement between the roller and the ballast in the lengthwise direction of the ballast, to thereby continuously squeeze together the insert by the rolling motion of the roller at the ballast, and controlling the pressure at the roller by an impedance measuring device connected with the ballast such that upon attaining a rated impedance the pressure acting at the roller is diminished and thereby obtaining an exact fine tuning of the ballast.
 2. The method as defined in claim 1, including the step of applying the contact pressure of the roller by a pressurized fluid medium operated piston.
 3. The method as defined in claim 1, including the step of applying the contact pressure of the roller by a lever arrangement.
 4. The method as defined in claim 1, further including the step of raising the roller away from the ballast upon attaining the rated impedance of the ballast.
 5. The method as defined in claim 1, including the step of displacing the ballast in lengthwise direction beneath the roller.
 6. The method as defined in claim 5, including the step of employing pressurized fluid operated piston means for displacing the ballast. 